1. Field of the Invention
The present invention relates to a servo information writing system and more particularly a servo information writing system which, even with no clock information stored in an information recording disk received in a cartridge, can write to the information recording disk servo information corresponding to the state of rotation of the disk in the cartridge when the cartridge is loaded into the writing system.
2. Description of the Related Art
Heretofore, for writing servo information to a magnetic recording medium such as a hard disk, there has been used such a servo information writing system as will be mentioned. First, using a clock head, clock information is written to an area of the magnetic recording medium which area is not used for the recording of data, for example, the outermost peripheral area and then the clock information is reproduced by a clock head to obtain the clock information (clock pulse).
With the clock information thus obtained as a cycle, a servo information writing head writes servo information to a sector head on the magnetic recording medium.
In this connection, reference is here made to FIG. 2, which is a schematic configuration diagram showing an example of configuration of a known servo information writing system.
As shown in FIG. 2, the known servo information writing system comprises a magnetic recording medium for example a hard disk 21, a spindle motor 22, a disk loading portion 23 connected to the spindle motor 22 for rotating the hard disk 21 as loaded onto the disk loading portion, a clock head (first head) 24 for writing clock information to the hard disk 21 and reading the clock information written in the hard disk 21, pattern signal (servo information) writing heads (second head) 25 for writing a pattern signal (servo information) to a second predetermined area of the hard disk 21, and a pattern signal generator (servo information forming section) 26 which receives the clock information read by the clock head 24, generates a pattern signal (servo information) based on the clock information and supplies the pattern signal (servo information) to the pattern signal (servo information) writing heads 25.
The servo information writing system having the above configuration operates in the following manner.
After the hard disk 21 has been loaded onto the disk loading portion 23, the spindle motor 22 is rotated to rotate the disk loading portion 23 which is connected to the rotating shaft of the spindle motor, with the result that the loaded hard disk 21 also rotates at the same time. At this time the clock head 24 writes clock information to an area of the hard disk 21 which area is not used for the recording of data, for example the outermost peripheral area. Then, the hard disk 21 with the clock information thus written therein is rotated by the operation of the spindle motor 22, while the clock information written in the hard disk 21 is read by the clock head 24 and the thus-read clock information is fed to the pattern signal generator 26. With the clock signal thus fed as a cycle, the pattern signal generator 26 forms a pattern signal (servo information) and transmits the thus-formed pattern signal (servo information) to the pattern signal writing heads 25, which in turn write the pattern signal to a sector head of a track on the hard disk 21. In this way there is performed writing of a required pattern signal (servo information) to the hard disk 21.
According to the recent trend, it has become popular to use a magnetic recording medium, e.g. a 3.5-inch floppy disk in which an information recording medium is accommodated within its cartridge case, together with a hard disk.
In such a 3.5-inch floppy disk, a shutter is provided in an opening portion of the cartridge case to prevent deposition of dust and the like on the surface of the information recording medium. For writing or reading information, the shutter is opened and a magnetic head is brought into contact with the information recording medium to write or read information to or from the information recording medium.
For writing servo information to such a 3.5-inch floppy disk by using the foregoing conventional servo information writing system, it is required to keep open the shutter disposed in the opening portion of the cartridge case and bring both the clock head 24 and pattern signal writing head 25 into contact with the information recording medium through the opening portion, with the result that the available data area in the information recording area is narrowed by an amount corresponding to the width which the clock head 24 occupies, thus giving rise to a problem that the storage capacity of the information recording medium is decreased.
If a second opening to be used exclusively for the clock head 24 is formed in the cartridge case and the clock head 24 is contacted with the information recording medium through the second opening, the above-mentioned decrease in storage capacity may be avoided. However, if the second opening is formed in the cartridge case and a second shutter is provided in the second opening, there will arise another problem that the number of components so much increases and hence the manufacturing cost of the 3.5-inch floppy disk rises.
There also is known other means for solving the problem in question. According to this means, a precision type encoder is attached to a drive shaft for rotating the magnetic recording medium at the time of loading of the same medium and clock information is obtained from information read by the precision type encoder during rotation of the magnetic recording medium, thereby omitting the use of the clock head 24. However, this means involves another problem that the precision encoder is usually expensive and cannot freely select its clock frequency.